Almost all Americans have premarital sex, says a report published Tuesday that analyzes federal data over time and suggests programs focusing on sexual abstinence until marriage may be unrealistic.

"The reality of the situation is that most people had premarital sex, and it's been that way for several decades," says Lawrence Finer, director of domestic research at the Guttmacher Institute, a New York City-based non-profit organization that studies reproductive and sexual health.

The study, which used statistics from the 1982, 1988, 1995 and 2002 National Survey of Family Growth, asked about 40,000 people ages 15-44 about their sexual behavior and traced the trends in premarital sex back to the 1950s.

Of those interviewed in 2002, 95% reported they had had premarital sex; 93% said they did so by age 30. Among women born in the 1940s, nearly nine in 10 did. At the same time, people are waiting longer to marry; 2005 data show median age at first marriage is just over 25 for women and 27 for men.

The study may fuel the debate over efforts by the federal government and others to fund programs that encourage abstinence until marriage. Such programs stress that abstaining from sex is the only effective or acceptable way to prevent pregnancy or disease.

Finer says the data suggest that abstinence programs face an "extremely high hurdle. … Is it really feasible to make it normative behavior to have everyone wait until they're married to have sex?" He says the margin of error is less than one percentage point.

This fall, the federal government clarified its guidelines for millions of dollars in 2007 federal money available to the states for abstinence-only programs. The message that such funds, which previously have focused on preteens and teens, would now also target unmarried adults up to age 29 stirred controversy after Wade Horn, assistant secretary for children and families at the Department of Health and Human Services, explained that the revision was aimed at making sure states knew money would be available for 19- to 29-year-olds because more unmarried women in that age group are having children.

Horn was unavailable for comment Tuesday.

But a fellow in family and culture issues at the Heritage Foundation, a conservative think tank based in Washington, D.C., that supports abstinence-only legislation, blasts the report as "an attack on abstinence."

Heritage fellow Pat Fagan says releasing the study late in the year is "part of a major Congressional battle about to start in January and February … to get rid of abstinence funding."

Finer says he had no control over when the study was published. It appears in the January/February 2007 issue of Public Health Reports, a bi-monthly, peer-reviewed journal of the U.S. Public Health Service, and also was posted on the Internet on Tuesday.

Steve Conley, a sex therapist and executive director of the 2,000-member American Association of Sexuality Educators, Counselors and Therapists in Ashland, Va., says he's not surprised by the data. "It fits with other trends we've been seeing," he says.